This invention relates to a liquid crystal display device, and more particularly to a reflective-type liquid crystal display device having a reflector on which a plurality of convex portions are formed and a method of manufacturing the reflector. Such liquid crystal display devices (hereinafter LCDs) using a reflector on which a plurality of convex portions are formed increase the viewing angle characteristic.
FIG. 1 is a schematic sectional view of a traditional reflective-type LCD having a rough reflector with Guest-Host driving mode. The LCD includes first and second substrates 11 and 12, a liquid crystal layer 13, a color filter layer 14 between the first and second substrates, a plurality of convex portions made of a photosensitive resin 15 formed on the second substrate 12, a pixel electrode 16 functioning as a reflector and formed on the convex portions, and a counter electrode (not illustrated) made of a transparent material such as Indium Tin Oxide (ITO) formed between the liquid crystal layer 13 and the first substrate 11.
FIGS. 2a-f represent a method of manufacturing the reflector of FIG. 1. The method includes the steps of first forming a photoresist layer 17 by spin coating photosensitive resin on substrate 12 as shown in FIG. 2a. Photoresist layer 17 is then exposed with ultraviolet light (indicated by arrows) from the upper side while blocking photoresist layer 17 with a mask 18 having a plurality of holes A and B as shown in FIG. 2b. Thereby, a plurality of convex portions, in which each convex portion has a size different from that of the neighboring convex portion, are formed on the second substrate 12 as shown in FIG. 2c. The convex portions are thermally treated so that the height of the convex portions is different as shown in FIG. 2d. Next, an over-coating layer 19 is formed by spin coating polymer resin as shown in FIG. 2e. Finally, a pixel electrode 16 is formed by sputtering Al, Ag, or the like as shown in FIG. 2f.
Referring again to FIG. 1, we describe the movement of the reflective-type LCD having a rough reflector with Guest-Host driving mode. When a voltage is not applied to the device, as shown in state I, the light is blocked by dichromatic dyes within the liquid crystal layer 13, and the device is thereby darkened. When a voltage is applied to the device, as shown in state II, the light through the first substrate 11 is reflected on the pixel electrode 16 after passing through the color filter layer 14 and liquid crystal layer 13. When reflected, the light is also diffused from the surface of the reflector, which has a fine geometrical structure, so that the reflected light is brighter than the original light that passed through the liquid crystal layer 13, the color filter layer 14 and the first substrate 11. As a result, the viewing angle and brightness are increased.
In LCDs, however, the process for making a plurality of convex portions requires one or two complex photolithography steps corresponding to the convex portion size, and the result of the process may be unstable. Further, an electric field between the pixel electrode and the counter electrode is distorted by multiform of the liquid crystal arrangement. As a result, it is impossible to provide a correct image to user despite of the increase in viewing angle and brightness.